Conventional spring-loaded contact probes generally include an outer receptacle, a movable plunger, a barrel containing the plunger, and a spring for biasing the reciprocating travel of the plunger in the barrel. The plunger is commonly biased outwardly a selected distance by the spring and may be biased or depressed inwardly of the barrel, a selected distance, under force directed against the spring. The plunger generally is solid and includes a head or tip for contacting electrical devices under test. Such conventional contact probes are generally referred to herein as three-component probes, since they have a receptacle, barrel and plunger.
In conventional devices, the barrel is mounted within the receptacle with the plunger extending outwardly from the receptacle. Preferably, the barrel is removably mounted in the receptacle, so that should damage occur to the barrel or plunger, replacement is possible. Usually, the receptacle is permanently or semi-permanently mounted in an array within a tester. Electrical wiring may be attached to the receptacle, for electrical communication between the receptacle and the testing diagnostic equipment. Preferably, the probe member, barrel and receptacle are manufactured from electrically conductive materials, so that an electrical circuit is maintained between the electrical device under test and test equipment, by means of the contact probe.
When such electrical probes are used, generally a contact side of the electrical device to be tested is brought into pressure contact with the tip of the plunger for maintaining spring pressure against the electrical device. After the electrical device has been tested, the pressure exerted by the spring probes is released and the device is removed from contact with the tip of each probe. In conventional systems, the pressure is released by moving the electrical device and probes away from one another, thereby allowing the plungers to be displaced outwardly away from the barrel under the force of the spring within the barrel, until an enlarged-diameter section of the plunger engages a crimped end portion of the barrel.
The process of making a conventional spring probe involves separately producing the compression spring, the barrel and the plunger. The compression spring is wound and heat treated to produce a spring of a precise size and of a controlled spring force. The plunger is typically heat treated and sometimes the barrels are heat treated. All components are subjected to a plating process to enhance conductivity. The spring probe components are assembled either manually or by an automated process. During assembly, the compression spring is first placed in the barrel, the plunger is then inserted into the barrel to compress the spring, and the barrel is roll crimped to retain the plunger. In use, the completed spring probes are commonly inserted into an outer receptacle for retaining the probe in a fixture or the like.
A problem with conventional spring probes is that for certain test sites the plunger may mark or damage the site upon contact. This problem stems largely from the material which makes up the test site, such as for example, ball grid array integrated circuits tend to have softer material comprising solder balls which constitutes the test sites.
Another problem which exists for certain convention spring probes is that a good biasing action with the inside of the barrel is difficult to form, thereby making the electrical path less efficient for transmitting the test signals to the external test electronics. Both of these problems stem from the current designs for the plunger of the spring probes.
Consequently, a need exists for an improved spring probe which eliminates the disadvantages associated with conventional spring-loaded contact probes.